Cytotoxic Fatty Acid from Pleurocybella porrigens

Abstract

The fungus Pleurocybella porrigens (called 'sugihiratake' in Japanese), which is a basidiomycete of the Trichoromataceae family, is a lignicolous agaric mushroom that produces pure white, relatively small pleurotoid fruiting bodies on rotting conifers, often in abundance.1) This edible mushroom grows during the late summer and autumn and is native to all districts of Japan, including the Tohoku and Hokuriku areas. P. porrigens was suspected to cause acute encephalopathy including coma and spasm in the Tohoku and Hokuriku areas in 2004.2-4) We have recently reported that an intraperitoneal administration of a hot water extract of P. porrigens caused acute toxic death with hemorrhagic anemia in mice within 24 h, and the toxicant was in part a thermolabile high molecule contained in this mushroom. 5) However, the toxic constituents responsible for patients with critical encephalopathy and nephrosis have not yet been clarified. In this study, we therefore isolated the toxic constituents from P. porrigens, and report here the isolation and structural elucidation of a new ketonic fatty acid conjugated with porrigenic acid (1) and its cytotoxic activity. Results and DiscussionThe MeOH extract of P. porrigens (2.5 kg fresh weight) was partitioned between EtOAc and H 2 O, and the EtOAc layer was subjected to bioassay-guided fractionation with repeated flash column chromatography on silica gel and ODS and further purified by HPLC equipped with an ODS column to afford new compound 1.Compound 1 was obtained as a colorless solid, and its molecular formula, C 18 H 30 O 4 , was established from HR-FAB-MS, which gave a pseudomolecular ion peak at m/z 311.2214 [MϩH] ϩ . The 13 C-NMR, DEPT, and HMQC spectra (Table 1) of 1 showed signals of one methyl, 10 methylenes, five methines, and two quaternary carbons including a carboxylic acid (d 177.9, C-1) and a ketone (d 203.7, C-9), respectively. The presence of two conjugated E,E-form enone systems was revealed by the 1 H-NMR spectrum ( . Furthermore, the UV spectrum of 1 displayed a l max at 273 nm.6) The 1 H-NMR spectrum (Table 1) showed signals at 0.92 (3H), 1.33 (10H), and 1.59 (6H) ppm, which can be attributed to the terminal methyl to methylene groups of aliphatic chains. HMBC correlations were observed at H-2/C-1, C-3, C-4; H-8/C-6, C-7, C-9, C-10; H-10/C-9; H-11/C-9; H-17/C-15, C-16, C-18; and H-18/C-16, C-17. Further analysis of EI-MS data indicated that notable fragment ion peaks were observed at m/z 57, 87, 139, and 167. The locations of a carbonyl carbon (d 203.7) at C-9 and an oxygenated methine carbon (d 72.6) at C-14 were identified from the HMBC spectrum and EI-MS analysis (Fig. 2). Based on the above data, compound 1 was determined to be (10E,12E)-14-hydroxy-9-oxo-10,12-octadecadienoic acid. A racemic mixture of 1 was isolated from the same mushroom by Amakura et al. The new conjugated ketonic fatty acid, porrigenic acid (1), was isolated as a cytotoxic constituent of Pleurocybella porrigens. The structure of 1 was elucidated using spectroscopic methods including...

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